Analysis on the Loss and Deficiency of the Flat Plate
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As a printing plate which is one of the five elements of lithography, the influence on the quality of printed matter in printing is very important. In the current lithographic plate making operation, although the CTP plate making method develops rapidly, the traditional printing method is still the main form of lithographic production. In the printing operation, the loss and illusion of the printing plate dot are common faults. The reasons and solutions for this common fault when using the positive-working PS version of the printing plate are discussed briefly for peer reference.
First, the original factor
In the lithographic printing plate, the original version is the copy object, and the quality of the original plate will directly affect the quality of the printing plate. The following factors of the original plate will cause the dot on the printing plate to be lost and falsified.
1. The original version is mistaken for Zhengyang
In lithography, since lithography is indirect printing, one of the characteristics of lithographic printing is that it is reversed, so it is decided to use the reverse original when lithographic printing, but there are quite a few small output organizations. The business level is not high, and the printing process is not well understood. The original version for lithographic printing is often output as forward film. With this original version, it is difficult to avoid the vacancy of the outlets and the loss of small outlets. Therefore, improving the business level of the exporters and enhancing their understanding of the printing process is something that some exporting organizations should do.
2, the original density is low
In the film output process, due to insufficient film exposure or overexposure, the original density value is lower than the density required by the printing plate (generally, the original density value is about 3.0). If the original density value is slightly lower than the required value, the exposure time can be reduced to reduce the degree of dot loss when printing, but if the original density value is too low, only the original version is replaced.
3, the film outlet in the middle of the virtual
In one printing, the author found that the printing plate was always not inked. It used a lot of methods to no avail. Later, the original version was observed with a high magnification magnifying glass, and it was sent to the middle of the original dot to make a virtual copy, which caused the printing plate to be hollow when printing. Ink. This may be caused by improper focusing of the recording head of the imagesetter at the time of film output.
Second, the dot loss and faint phenomenon caused by overexposure during the printing process
The exposure time of the printing plate is related to the depth of the printing plate. The short version of the positive version of the PS version is shorter, the printing plate is deeper, and the layout is easy to get dirty; on the contrary, the exposure time is long, because the version of the dot is lost and imaginary, because the plate is shallow, It is not easy to apply ink when printing. Therefore, the proper exposure time for printing is extremely important.
If you replace the plate lamp and adjust the lamp distance, use different brands of photographic plates or different brands of the same brand but different batches. Before the official printing, apply continuous adjustment ruler, dot ladder or other test strips. The PS version to be used is tested and the proper exposure time is found to ensure the correct transfer of the dots during the printing process.
In the actual printing, quite a lot of operators choose the exposure time based on experience, and in the process of printing, the method of lengthening the exposure time is often used to avoid the dirty surface on the plate and remove the small dirty spots on the plate. The impact of the edition is not obvious, but for the dot version, it will cause the dot to be lost and falsified.
Third, there is a gap between the original and the photosensitive plate
1. Insufficient vacuum
Before the exposure, it is necessary to vacuum the drying machine, so that the original and the photosensitive plate are closely attached. If the vacuum is improperly set or the vacuum pump fails, the suction pipe ages and ruptures, and the sealing strip of the drying machine's drying chamber aging and ruptures, there will be insufficient vacuuming. The original plate and the photosensitive plate cannot be closely attached to cause the dot to be lost and imaginary.
2. There is dirt between the original and the photosensitive plate.
Before the printing, the film should be cleaned. If the cleaning is not complete, there will be small sand particles and other objects attached to the film. After the printing plate is developed, dirty spots will appear, and the surrounding dots of the dirty spots will be lost and faint. .
3, the original version
In many editions of books and magazines, printers often output small-format films for cost reasons, and then use the manual imposition to form a large version. When splicing a large version, the edges of the small film may have "wavy edges" or "burrs" when cutting, and these phenomena will cause a gap between the original and the photosensitive plate, so that during the printing process The dot appears to be lost and faint.
In addition, since the tape is used to fix the small film on the base when the group is assembled, if the tape is too close to the text or the image area, the printing will also cause the loss of the dot, the illusion or the lack of pen break.
4, when the sun is covered, the cover is too close to the original
In the printing process, sometimes you need to use a four-film or even an eight-open film to make the printing plate. In most small printing factories, this situation is usually done by hand. The way to solve it. For example, in the case of a four-open film, the exposure plate needs to be exposed twice. At each exposure, half of the photosensitive plate needs to be covered. If the cover is too far from the original position, it will cause waste of paper when printing; but if it is too close, the original will not be in close contact with the photosensitive plate during the pumping process, so that the dots on the plate appear. Lost and faint. Therefore, when connecting to the sun, choose the appropriate seam size according to the paper size used for printing.
Fourth, other factors
1, the photographic version or the original version has creases
When printing on the plate, the original or the photographic version has creases, and the two can not be closely attached together. In the process of printing, the dots will be lost and vain. Therefore, it is very important to carefully check the original and photosensitive plates before printing.
2, double exposure
Double exposure is a book edition, especially a method often used to remove dirt when using the original plate. This method of removing dirt is to use the scattering film to refract light to expose the dirty lines and dirty spots generated by the edge of the film. However, this method also causes the small dots to be lost. Therefore, it is not suitable to use the image plate twice. exposure.
3, overexposure
Excessive development will not only cause the small dots to be lost or falsified, but also reduce the printing durability of the printing plate.
4, the revision is inadvertent
When the revision is made, if the repairing paste or the repairing solution is eroded to the graphic part, it is inevitable that the dot will be lost and vain. When repairing the plate, the repairing paste or the repairing liquid medicine should be rinsed off in time to avoid damage to the layout.